a. Field of the Invention
Liquid ion exchange treatment of zinc values.
B. Description of the Prior Art
In presently practiced commercial zinc hydrometallurgy zinc sulfide concentrates containing several associated metals are given an oxidizing roast, thereby producing an SO.sub.2 laden gas, which can be sent to a sulfuric acid plant, and a calcine containing zinc values. The calcine is then leached with sulfuric acid. The sulfate solution obtained from leaching carries most of the associated metals along with the zinc and must go through a complicated series of impurity precipitation steps, some involving additives, prior to treatment by electrolysis. The spent electrolyte stream from electrolysis is then returned to the leaching operation and incompletely precipitated impurities and additives that build up in such a sulfate system are troublesome and involve high-cost removal systems.
In liquid ion exchange purification efforts, severe problems are encountered when a precipitate is formed and stays in the system during the solvent extraction (aqueous to organic) step. Precipitates cause emulsification at the aqueous-organic interface, render phase separation less complete, and entail substantial costs for precipitate removal. Co-extraction of other metals with the desired metal also poses substantial problems in the art. Ion exchange systems for purification of zinc from strong acid solutions (for example: sulfate, chloride, nitrate) are pH dependent, and cannot be successfully carried out for concentrated zinc feedstreams without costly neutralizing additives. Various attempts have been made to solve the problems encountered in zinc liquid ion exchange systems. U.S. Pat. Nos. 2,992,894; 3,573,182; and 3,479,378 are examples of attempts to deal with the problems encountered in liquid ion exchange technology for the treatment of zinc.